Ultra high frequency mixer circuit



Dec. 30, 1947. w. A. MONTGOMERY 2,433,335

ULTRA HIGH FREQUENCY MIXER CIRCUIT- Filed Oct. 14, 1942 as. H. 15 l6 3 j I u ]3-:: 23

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INVE/VTCR wpmoumomzkg ATTORNEY Patented Dec. 30, 1947 ULTRA HIGH FREQUENCY MIXER CIRCUIT William Alan Montgomery, London, England, as-

signor to Standard Telephones and Cables Limited, London, England, a British company Application October 14, 1942, Serial No. 462,025 In Great Britain September 26, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires September 26, 1951 9 Claims.

The present invention relates to frequency mixing arrangements and it has for its object to provide an arrangement which is particularly suitable for use at ultra high frequencies. In particular it provides an improved arrangement for coupling a coaxial line tube cavity resonator to a triode and applying the input frequencies to be mixed to the cavity resonator.

According to the invention a frequency mixing arrangement for use at ultra high frequencies comprises an input resonant chamber electrically coupled to the input electrode of a thermionic discharge device comprising at least an anode, a cathode, and a control grid, said input electrodes cathode and control grid being located within said chamber, couplings into the chamber for the respective frequencies to be mixed and an output circuit for the resultant frequencies screened from the input circuit.

From a more specific aspect the invention resides in a frequency mixing arrangement for use with ultra high frequencies comprising an input resonant chamber containing the cathode and control grid of a thermionic discharge device, said cathode being connected or coupled, as regards the frequencies to be mixed, to said chamber, and the control grid being provided with an auxiliary metallic member extending outside the enclosing envelope of the discharge device and connected or coupled, as regards the frequencies to be mixed, to the wall of said chamber, couplings to said chamber for the respective frequencies to be mixed and an output circuit for the desired resultant frequency screened by said metallic member from the input circuit.

In an embodiment of the invention the chamber comprises a hollow resonator, such as a length of coaxial conductor line closed at one end and electrically connected or coupled to the input electrodes at the other end, the cathode of the said discharge device being connected to the inner conductor and'the control grid being coupled or directly connected to the outer conductor.

The invention will be better understood from the following description taken in conjunction with the accompanying drawing which shows the preferred embodiment.

Referring to the drawing, the inputchamber I comprises an inner conductor 3 and an outer conductor 2 of a coaxial transmission line which is closed at one end by a metallic plate [0. In this particular embodiment the outer conductor is made in two parts telescoping one within the other so as to be adjustable to tune the cham ber into resonance with one of the input frequencies.

The thermionic electric discharge device is indicated at 4 and its construction is fully described in the specification of the copending application of John Foster, Serial No. 445,509, filed June 2, 1942, Pat. No. 2,419,544, granted Apr. 29, 1947. This discharge device comprises an indirectly heated cathode .5 connected to the inner conductor 3 of the chamber and heated by means of a filament 6, the leads to the filament comprising the inner conductor 3 and a further conductor it running through the interior of the inner conductor 3. The control grid of the thermionic discharge device is indicated at l and is provided with a metallic, preferably copper, annular disc 8 which extends outside the envelope of the device. The anode of the discharge device is indicated at l2. The outer conductor 2 of the chamber is provided with a flange i3 which is connected so as to form a capacitative coupling, as shown in the drawing,

with the metallic annular disc 8 of the grid. When a capacitative coupling is used as shown in the drawing discs of mica M are inserted between the flange l3 and the member 8'. The two frequencies which are to be mixed, for instance, an ultra high frequency signal and the frequency generated by a local oscillator, are applied to the input chamber by means of the coaxial circuits l5 and I6 as shown. The outer conductors of these two circuits are directly connected to the outer conductor of the chamber and the inner conductors are coupled to the inner conductor 3 of the chamber by capacitative couplings shown at l1 and i8. The position of the frequency input leads I5, [6 along the longitudinal axis of the chamber is chosen so that when the chamber is tuned to one of the frequencies the most efficient point of application of both the frequencies is used.

The output circuit from which the intermediate frequency due to the heterodyning of the two input frequencies is obtained is housed within a metallic screen box indicated at l9 which is coupled capacitatively to the annular member 8 of the grid. The anode I2 is coupled to the first valve of the intermediate frequencyamplifier stage indicated at 20 by means of a resistancecapacity coupling 2|, 22. The high tension supply to the anode of theclischarge device 4 is provided through the intermediate frequency tuning coil 23 which is resonated with the stray capacities of the circuit of the intermediate frequency and decoupled to earth through a capacity 24,.the

shield being an effective radio frequency ground.

An additional decoupling capacity 25 may be connected between the intermediate frequency amplifier screening box 19 and the metallic meme. her 8 of the grid 1 of the discharge device 4. The grid bias is provided through the lead G. B, in any suitable manner to the device 4. In a practical use of this valve as a centimetre wave mixer it was found that the valve operated best at zero grid bias and the highest permissible anode voltage, that is, working on the straight part of its characteristic.

The triode 4 operates for best results as a grid detector. The two signals to be heterodyned are applied to the coaxial cavity resonator l in which standing waves of the two frequencies are set up. These are applied as a voltage variation via condenser M, between the cathode and grid of the triode. The bias applied to the grid is adjusted so that the tube operates on the curved part at the top of the plate current-grid voltage characteristic. With the grid at Zero or ground poten- ,tial and a high plate potential most of the tube detected signal is obtained from the straight part of the tube characteristic. The inductance coil 2.3 is tuned to the stray capacities in the circuit at the intermediate frequency resulting from the beating together of the two input frequencies so that the intermediate frequency is passed to the I. F. stages and the ultra-high frequencies highly attenuated.

The function of the mica sheets M on either side of the grid disc 8 to decouple the input and output circuits from each other as far as the direct potential applied to the grid G. B. The capacity l4 between the resonator l and the grid disc 8 coupled the ultra-high frequencies in the resonator l to the grid. The capacity I4 between the grid disc 8 and both the resonator l and the metal box l9 decouples the grid voltage from the said container and resonator. In addition to the tuning of coil 23 whereby the ultra high frequencies are highly attenuated in the output circuit the arrangement of grid disc and metallic box It affords a good shielding arrangement around the output circuit.

The arrangement as defined herein affords an efficient and compact mixer of ultra high frequencies. While I have described above the principles of my invention in connection with specific apparatus and operating conditions it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention.

It will be observed that by means of the metal! lic member 8 the input circuit is completely screened from the output circuit.

What is claimed is:

1. An arrangement for mixing two ultra high frequencies carried by respective transmission lines comprising an electron discharge device having at least a cathode,control grid and anode, a'hollow resonator coupled between said cathode and control grid, means for coupling said trans- .mission lines to said resonator, means for tuning said resonator to one of the said ultra high fre-. quencies, a circuit coupled between the anode and grid of said electron discharge device-for obtaining the intermediate frequency resulting from ixing said ultra high frequencies, and means adjacent said grid for shielding the said transmission lines from the said intermediate free quency circuit.

' 2. An arrangement for mixing two ultra high frequencies carried by respective transmission lines comprising an electron discharge device having at least a cathode, control grid and anode, a hollow resonator comprising a length of coaxial transmission line coupled between said grid and cathode, means for coupling the transmission lines carrying said ultra high frequencies to said length of coaxial transmission line, means for tuning said length of coaxial transmission line to one of said ultra high frequencies, a circuit coupled between said grid and anode for obtaining the intermediate frequency resulting from mixing said ultra high frequencies, and means adjacent said grid for shielding the said transmission lines from the said intermediate frequency circuit.

3. An arrangement for mixing two ultra high frequencies carried by respective transmission lines comprising an electron discharge device having at least a cathode, control grid and anode, a hollow resonator coupled between said grid and cathode, means for tuning said hollow resonator to one of said ultra high frequencies, means for coupling at least the transmission line carrying the other ultra high frequency to the most efficient point of application for that frequency on the resonator, and a circuit coupled between said grid and anode for obtaining the intermediate frequency resulting from mixing said ultra high frequencies.

4. An arrangement for mixing two ultra high frequencies carried by respective transmission lines comprising an electron discharge device having at least a cathode, control grid and anode, a hollow resonator coupled between said cathode and control grid, means for tuning said hollow resonator to one of said ultra high frequencies and means for coupling both of said transmission lines to the respective most efficient points of application on said resonator and a circuit coupled between said grid and anode for obtaining the intermediate frequency resulting from mixing said ultra high frequencies.

5. An arrangement for mixing two ultra high frequencies carried by respective transmission lines comprising an electron discharge device having planar cathode, control grid and anode electrodes located parallel to each other, said grid electrode being connected to a metallic disc extending through the envelope of the device, a length of coaxial transmission line provided at one end with a flange, and mounted with said flange in close proximity to said metallic disc 50 as to enclose the cathode of said discharge device, means for coupling the transmission lines carrying the ultra high frequencies to said coaxial transmission line, means for tuning said coaxial transmission line to one of the ultra high frequencies and a circuit coupled between said grid and anode for obtaining the intermediate frequency resulting from mixing the two ultra high frequencies.

6. An arrangement according to claim 5 fur ther comprising a screening box mounted in close proximity to the anode side of said disc to house said circuit coupled between said grid and anode.

'7. An arrangement according to claim 5 further comprising a sheet of insulating material between said disc and said flange to form a capacity coupling for ultra high frequencies between said grid and coaxial transmission line.

8. An arrangement according to claim 5 furthercomprising a screening box mounted in close proximity to the anode side of said disc and insulated therefrom to form a capacity coupling for intermediate frequencies between the grid and said circuit and said disc and flange having a space therebetween to form a capacity coupling for ultra high frequencies between said grid and coaxial transmission line.

9. An arrangement according to claim 5, wherein the outer conductor of said coaxial transmission line comprises two telescoping parts, one provided with said flange, and the other provided with a short circuiting plate at its end remote from said flange, whereby the coaxial line res- 10 onator can be tuned to the desired frequency by varying its length, and said means for coupling the transmission lines to said resonate-r comprises plates forming capacities with the central conductors of the coaxial line resonator, said transmission lines being connected to respective plates.

WILLIAM ALAN MONTGOMERY.

REFERENCES CITED The following references are of record in the 5 file of this patent:

UNITED STATES PATENTS Number Name Date Zottu Jan. 10, 1939 Potter Feb. 8, 1938 Southworth Feb. 1, 1938 Southworth Apr. 11, 1939 Linder Aug. 18, 1942 Smith Jan. 7, 1941 MacLean Mar. 25, 1941 

